1. Field of the Invention
The present invention relates to a method and an apparatus for producing a conductive material. Specifically, the conductive material according to the present invention is light transmittable and capable of shielding electromagnetic waves from microwave ovens, electronic devices, printed circuit boards, display devices such as CRT (cathode ray tube) displays, PDP (plasma display panel) displays, liquid crystal displays, EL (electroluminescence) displays, and FEDs (field emission displays), etc.
2. Description of the Related Art
The flat panel display (FPD) market has been rapidly growing due to increase in display size, demand for replacement of CRT, etc., and capacity to produce flat panel displays has been increased at high speed. Thus, it is necessary to increase capacity to produce materials for the FPDs, and particularly there is a demand for improving productivity of light transmittable, electromagnetic-shielding materials.
A technique, which comprises the steps of exposing and developing a photosensitive film having a silver salt emulsion layer, and subjecting the developed silver to a plating treatment to make the photosensitive film conductive or to increase the conductivity of the photosensitive film, is known as a method for producing the electromagnetic-shielding materials (see Japanese Laid-Open Patent Publication Nos. 2004-221564, 2004-221565, and 2006-012935, etc.) There is an increasing demand for rapid mass production using this technique, particularly for increasing plating reaction rate.
A chemical activating pretreatment, which comprises immersing a base material to be electroless-plated in an activating solution containing a noble metal such as Pd or a reducing agent such as sodium borohydride, is known as a method for increasing the plating reaction rate (see Japanese Laid-Open Patent Publication Nos. 2006-228836, 2006-228474, and 2006-228480).
However, in the chemical activating treatment using the noble metal solution, silver portions formed due to development fogging (corresponding to opening portions of a conductive film mesh-type, light transmittable, electromagnetic-shielding material) and portions other than the developed silver are chemically activated as well. The portions are inevitably covered with an unnecessary plated film (hereinafter referred to as a plating fog), whereby the light transmittability of the base material is disadvantageously reduced. Further, the plating fog is generated also due to contamination of the electroless-plating solution by the activating liquid or falling of an active core in an electroless plating solution, and causes deterioration of the electroless plating solution.
The immersion treatment using the reducing agent solution is disadvantageous in that, for example, silver portions formed due to development fogging causes the plating fog, the reducing agent per se is oxidation-degraded, and a large amount of hydrogen is generated. Thus, also the immersion treatment is not suitable for rapid production of the conductive materials.